2012 Articles

Variations in the Abundances of Potassium and Thorium on the Surface of Mercury: Results from the MESSENGER Gamma-Ray Spectrometer

Solomon, Sean C.; Peplowski, Patrick N.; Lawrence, David J.; Rhodes, Edgar A.; Sprague, Ann L.; McCoy, Timothy J.; Denevi, Brett W.; Evans, Larry G.; Head, James W.; Nittler, Larry R.; Stockstill-Cahill, Karen R.; Weider, Shoshana Z.

A technique for converting gamma-ray count rates measured by the Gamma-Ray Spectrometer on the MESSENGER spacecraft to spatially resolved maps of the gamma-ray emission from the surface of Mercury is utilized to map the surface distributions of the elements Si, O, and K over the planet's northern hemisphere. Conversion of the K gamma-ray count rates to elemental abundances on the surface reveals variations from 300 to 2400 ppm. A comparison of these abundances with models for the maximum surface temperature suggests the possibility that a temperature-related process is controlling the K abundances on the surface as well as providing K to the exosphere. The abundances of K and Th have been determined for several geologically distinct regions, including Mercury's northern smooth plains and the plains interior to the Caloris basin. The lack of a significant variation in the measured Th abundances suggests that there may be considerable variability in the K/Th abundance ratio over the mapped regions.